The invention relates to a gas turbine engine, especially an aircraft gas turbine engine, with a compressor bearing chamber and a turbine bearing chamber. Barrier air chambers surround the bearing chambers that are supplied with oil. The barrier air chambers are supplied with a barrier air flow by a low-pressure compressor or fan and a high-pressure compressor. The flow passes at least partially into the associated bearing chambers through labyrinth seals and is conducted away from the bearing chambers through an oil separator, especially into the environment. Reference is made to Great Britain Patent document GB-B- 702 931 as an example of the prior art.
The seals provided in the bearing chambers for the shafts of a gas turbine engine between the bearing chamber wall as well as the shaft passing therethrough are necessary to prevent lubricating oil or an oil mist from entering the compressor or the turbine. This seal must be made contact-free, so that usually labyrinth seals are used which are, however, additionally traversed by a barrier air flow to achieve an optimum sealing effect. This barrier air flow comes from a barrier air chamber surrounding the bearing chamber through the labyrinth seals into the bearing chamber and is conducted out of the latter through an oil separator, preferably into the environment, but could also be used later in another fashion.
In order to ensure the flow of barrier air described above from the barrier air chambers into the bearing chambers and from the latter into the environment for example, a certain pressure drop is always required between the barrier air chambers and the environment, i.e. the pressure in the barrier air chambers must be larger by a certain amount than that downstream from the bearing chambers. Therefore, it is conventional to supply the barrier air chambers from the low-pressure compressor, which can also be designed as a fan, or from the high-pressure compressor with a barrier air flow. However, during the operation of a gas turbine engine, operating points can occur in which the pressure delivered by the low-pressure compressor or fan is not sufficient to deliver a barrier air flow which overcomes the flow resistances, for example, in the labyrinth seals, through the barrier air chambers, as well as the bearing chambers, and then through an oil separator and into the environment. Great Britain Patent document GB-B- 702 931 mentioned above therefore proposes to tap off the barrier air flow from the high-pressure compressor in these cases.
This known prior art is disadvantageous because not only is a separate switching valve required, with the aid of which the barrier air flow is tapped off either from the low-pressure compressor or fan or from the high-pressure compressor. Also this known prior art is disadvantageous because each of the bearing chambers is exposed at least temporarily to a relatively high-temperature barrier air flow, since, as is known, a definitely elevated temperature level prevails in high-pressure compressors.
There is therefore needed an improved and simplified manner of providing barrier air supply to a gas turbine engine, especially one for an aircraft gas turbine, having a compressor bearing chamber, a turbine bearing chamber and barrier air chambers surrounding the compressor and turbine bearing chambers. The barrier air chambers are supplied by a low pressure compressor or fan and a high-pressure compressor with a barrier air flow. The barrier air flow passes through labyrinth seals at least partially into an associated bearing chamber and is carried away from the latter through an oil separator.
These needs are met according to the present invention by a gas turbine engine wherein the compressor barrier air chambers are supplied by the low-pressure compressor or fan and wherein the turbine barrier air chambers are supplied with barrier air from the high-pressure compressor. The barrier air flow emerging from the compressor bearing chambers is mixed in an ejector with the barrier air flow emerging from the turbine bearing chambers. For an advantageous improvement, the oil separator can then be provided downstream from the ejector.
According to the present invention, therefore, the compressor bearing chambers are always exposed to a barrier air flow delivered by the low-pressure compressor or a fan, while the turbine bearing chambers are always supplied by a barrier air flow that is delivered by a high-pressure compressor. In this manner, first of all the switching valve known from the prior art can advantageously be eliminated without replacement. In addition, the compressor bearing chambers then always receive a relatively low-temperature barrier air flow so that these bearing chambers can also be made of a material that would not withstand high temperatures, for example magnesium. However, in order to make sure that in the event of insufficient delivery pressure from the low-pressure compressor or fan, a barrier air flow would nevertheless be supplied in the desired direction through the bearing chambers, according to the present invention an ejector or extractor is provided which draws-off the barrier air flow flowing through the compressor bearing chambers from these bearing chambers. The pressure potential still present in the barrier air flow from the turbine bearing chambers is utilized for this purpose. With this arrangement, not only is a sufficient barrier air flow ensured in both bearing chambers at all operating points but, in addition, the lubricating oil circuit of the gas turbine engine is only minimally heated since the compressor bearing chambers are exposed at all operating points to a relatively cold barrier air flow.
Of course, in further preferred embodiments, additional bearing chambers or the like using the principle according to the invention could reliably be provided with a barrier air flow. In addition, it may be sufficient for the compressor barrier air chambers, as is necessarily required by the design, to be located in the downstream area of the fan so that even without a separate barrier air supply line, a sufficient barrier air flow can pass from this fan into the compressor barrier air chambers. Moreover, in a barrier air supply system according to the invention, if the required oil separator is located downstream from the ejector, firstly this means that only a single oil separator is required and, secondly, this oil separator does not make itself felt in a harmful manner by reducing the pressure, i.e. upstream from the ejector or extractor a sufficiently high pressure level prevails to ensure the barrier air supply system according to the invention. This is also evident from the schematic diagram explained below of a preferred embodiment. Only those elements of a gas turbine engine according to the invention required for understanding have been included.